It has long been known that the brittle nature of poly(monovinylaromatic) polymers such as polystyrene is overcome by incorporating a minor amount of rubber. The rubber is largely incompatible with the polymeric vinyl compounds resulting in a two-phase system comprising a dispersed rubbery phase and a poly(monovinylaromatic) matrix.
One of the major variables in the preparation of such impact improved polymers is the selection of the particular rubber to be employed. Among the various rubbers mentioned in the patent literature are:
______________________________________ medium cis polybutadiene U.S. 3,868,434 styrene-butadiene-block copolymers U.S. 3,485,894 styrene-butadiene random copolymers U.S. 3,976,721 lithium-initiated styrene-butadiene copolymers U.S. 3,929,936 low styrene content styrene-butadiene copolymers U.S. 4,096,205 Blends of polybutadiene rubber and polyisoprene rubber U.S. 4,026,969 ______________________________________
Numerous other patents claiming advantages for certain rubbers or blends of rubbers are also known.
A novel rubber composition for use in making impact improved polymers has now been found. This rubber composition results in significantly improved impact properties, along with an unobvious morphological structure.